JPH07168095A - Triplet lens - Google Patents

Abstract

PURPOSE:To secure a small lens system, being high performance at a wide field angle and bright, with a triplet lens of 3-group/three sheet constitution, by forming at least one surface of both second and third lenses into aspheric surface, and making it satisfy a specific condition. CONSTITUTION:This triplet lens consists of a first lens L1 or positive meniscus lens directing a convex to the body side, a second lens L2 or biconcave lens, a third lens L3 or biconvex lens, and a stop S. In this constitution, at least one surface out of these second and third lenses L2 and L3 is formed into an aspheric surface, making it satisfy a conditional expression of 1X10<-5¦x1/f¦<1X10<-2>, 0.5<r5/f<1.1. Where, x1 is slippage, from the reference spherical surface, of the aspheric surface in at least one effective maximum diameter out of the aspheric surface, r3 is a radius of curvature of the body side of the third lens L3, and f is a focal distance of the whole system. In this connection, when this aspheric surface is used afterward the third surface, its effect grows larger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triplet lens having a behind diaphragm suitable for a lens shutter camera or the like.

[0002]

2. Description of the Related Art Conventionally, a triplet lens has been used in many lens shutter cameras because it has a small number of lenses and can obtain a relatively good optical performance and can be easily downsized.

Among the triplet lenses, a behind-aperture diaphragm lens system in which a diaphragm is arranged behind the lens system is
There are many conventional examples because the lens barrel structure is simple and it is advantageous for lens extension and exposure control.

However, since the degree of freedom in design is small with a small number of lenses such as a triplet lens,
With a lens system composed of only spherical lenses, there was a limit in achieving a wide-angle, bright, compact, and high-performance photographic lens. In particular, the deterioration of the performance from the middle of the angle of view to the periphery is remarkable, a lot of coma flare occurs, and at the same time the spherical aberration becomes large.

As a conventional example of a triplet lens using an aspherical lens in order to solve these problems, JP-A-59-34510, JP-A-59-160119 and JP-A-59-160120 are known. , JP-A-63-
The one described in Japanese Patent No. 96620 is known.

The photographing lenses described in these publications have a relatively bright and wide angle of view and a compact structure and have good optical performance by using an aspherical lens. However, these photographic lenses have an F number of about 3.5, which is not sufficient in terms of brightness.

Further, among the above-mentioned conventional examples, JP-A-59-59
160119, JP-A-59-160120, JP-A-63-96620, etc.
Since the aspherical amount of the aspherical surface is small, the aberration correction action is not sufficient, and the coma aberration is insufficiently corrected.

Furthermore, the taking lens disclosed in Japanese Patent Laid-Open No. 59-34510 uses an aspherical surface as the first lens.
When an aspherical surface is used for the first lens, it has a correcting effect on coma aberration, but the correction of spherical aberration is conspicuously insufficient, and it appears largely on the under side.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a triplet lens having a three-group, three-lens structure using an aspherical surface and having a high performance, a wide angle of view and a bright and compact lens system.

[0010]

The triplet lens of the present invention comprises, in order from the object side, a positive meniscus first lens having a convex surface facing the object side, a biconcave second lens, and a biconvex lens first. The lens system is composed of three lenses and a diaphragm, at least one surface of the second lens and the third lens is an aspherical surface, and satisfies the following conditions (1) and (2).

(1) 1 × 10 ⁻⁵ <| x ₁ / f | <1 × 10 ⁻² (2) 0.5 <r ₅ /f<1.1 where x ₁ is the aspheric surface The amount of deviation of the aspherical surface from its reference spherical surface in at least one effective maximum diameter,
r ₅ is the radius of curvature of the object side surface of the third lens, and f is the focal length of the entire system.

Generally, in a triplet lens, when the F number is brightened to about 2.8, the height of the axial marginal ray becomes large, the ray passing near the outer periphery of the lens is strongly bent, and large spherical aberration occurs. In addition to this, if the overall length of the lens system is suppressed to reduce the size of the lens system, the refracting power of each lens becomes strong, so that coma aberration occurs and performance around the screen is significantly deteriorated.

On the other hand, the aspherical lens has a large effect on the peripheral portion of the lens and therefore has an effect of correcting an axial marginal ray and an off-axis ray having a high ray height.

In the present invention, two problematic aberrations are simultaneously corrected. In this case, when it is performed using an aspherical surface, the effect is great if it is used on the third surface or later. When an aspherical surface is used as the first surface or the second surface, the off-axis ray passes only through the peripheral portion of the lens, so that the action of the aspherical surface acts only on the off-axis ray and therefore spherical aberration can be corrected. Can not. However, if an aspherical surface is used on the third surface or later, the action is well dispersed, and therefore both spherical aberration and coma can be corrected, and a high-performance taking lens can be realized.

Therefore, in the present invention, at least one of the surfaces of the second lens and the third lens is an aspherical surface. Then, at least one of the aspherical surfaces satisfies the above condition (1) so that the effect of using the aspherical surfaces can be maximized. That is, if the aspherical amount of at least one of the aspherical surfaces is within the range of the condition (1), the effect of the aspherical surface can be maximized, and spherical aberration and coma can be corrected well. . In a lens system such as the present invention, F / 2.8
In order to make a lens system of a certain degree of brightness, it cannot be realized by only a spherical surface, it is necessary to use an aspherical surface, and in order to satisfactorily correct these aberrations, it is necessary to satisfy the above condition (1). If the range of this condition is exceeded, the coma aberration cannot be corrected well, and the lower limit of the condition (1) is 1 × 10 ^−5.
If it exceeds, the coma aberration will be undercorrected and the upper limit of 1 × 10
^When it exceeds ^-2 , high-order aberrations occur. Regarding spherical aberration, if the lower limit of the condition (1) is exceeded, the aberration will be undercorrected, and if it exceeds the upper limit, the aberration will be overcorrected.

In the above condition (1), the lower limit value is 1
It is more desirable to set it to × 10 ⁻⁴ .

Further, in order to keep the coma aberration excellent, the condition (2) is satisfied in the present invention. This condition (2) defines the radius of curvature of the object-side surface of the third lens. If the upper limit of 1.1 of this condition (2) is not exceeded, the third lens can have a certain degree of refracting power, and therefore the back focus can be shortened and the lens system can be shortened. The lower limit of 0.
When it exceeds 5, the ray is strongly bent on this surface, and the bending of coma becomes large. It is more desirable to set the upper limit value to 1.0 in the condition (2).

Next, in the present invention, the following condition (3) is satisfied.
It is desirable to satisfy (4).

(3) 0.5 <f ₁ /f<0.95 (4) −3.5 <f ₁₂ /f<−0.8 where f ₁ is the focal length of the first lens and f ₁₂ is It is a combined focal length of the first lens and the second lens.

The condition (3) defines the refractive power of the first lens, and the condition (4) defines the combined refractive power of the first lens and the second lens. By properly arranging the refracting powers of these lenses in this way, the Petzval sum can be suppressed to be small and the image surface property can be kept good. Therefore, it is desirable to satisfy these conditions (3) and (4).

The condition (3) is mainly necessary for correction of spherical aberration and astigmatism. When the lower limit of 0.5 of the condition (3) is exceeded, the spherical aberration falls to the under side or barrel distortion. Becomes big. Further, the sagittal image plane and the meridional image plane are greatly inclined to the over side, and the astigmatic difference is further increased. If the upper limit of 0.95 to condition (3) is exceeded, spherical aberration will be undercorrected on the overside.

The condition (4) is for keeping the Petzval sum at an appropriate value and simultaneously reducing astigmatism. If the lower limit of -3.5 to condition (4) is exceeded, the Petzval sum will have a large positive value, and it will be impossible to suppress field curvature. If the upper limit of -0.8 to condition (4) is exceeded, the Petzval sum will become small and the sagittal image plane will be overcorrected.
Since the meridional image plane is of high order and is largely inclined to the under side, the astigmatic difference becomes large and it becomes difficult to correct it.

Next, in order to satisfactorily correct spherical aberration and coma, it is desirable to satisfy the following condition (5).

(5) 1 × 10 ⁻⁶ <| x ₂ / f | <1 × 10 ⁻³ However, x ₂ is the amount of deviation of the aspherical surface from the reference spherical surface at the position of 1/2 of the effective radius. .

In order to correct spherical aberration and coma better, it is preferable that the aspherical surface satisfies the condition (1) and at the same time satisfies the above condition (5). That is, the condition (5) has the same effect as the condition (1), and if x ₂ is in the range of the condition (5), both spherical aberration and coma can be favorably corrected.

[0026]

EXAMPLES Examples of triplet lenses according to the present invention will be described below. Each of the embodiments of the present invention has a configuration as shown in FIG. 1, and in order from the object side, the first lens L ₁ is a positive meniscus lens having a convex surface facing the object side, and the second lens L _{2 is a} biconcave lens. And a third lens L _{3 which} is a biconvex lens, and a diaphragm S.

Next, the first embodiment of the present invention having the above-mentioned structure
7 shows the data of Example 7. Example 1 f = 100, F / 2.78, 2ω = 64.7 °, f _B = 77.835 r ₁ = 32.466 d ₁ = 10.85 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 74.59 d ₂ = 4.82 r ₃ = -86.321 d _{3 = 2.34 n 2 = 1.689 ν} 2 = 31.08 r 4 = 34.271 d 4 = 3.58 r 5 = 90.834 d 5 = 6.81 n 3 = 1.799 ν 3 = 42.24 r 6 = -60.477 ( aspherical) d ₆ = 3.18 r ₇ = ∞ (aperture) Aspherical coefficient E = -0.41866 × 10 ^-6 , F = 0.71905 × 10 ^-9 , G = -0.653
9 × 10 ^-11 │x ₁ /f│=3.26×10 ^-4 , │x ₂ /f│=1.35×10 ^-5 f ₁ /f=0.706, f ₁₂ /f=-1.279, r ₅ / f = 0.90
8

Example 2 f = 100, F / 2.84, 2ω = 65.5 °, f _B = 78.726 r ₁ = 32.319 d ₁ = 11.51 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 59.822 d ₂ = 4.5 r ₃ = -82.013 d ₃ = 2.37 n ₂ = 1.688 v ₂ = 31.08 r ₄ = 35.56 d ₄ = 3.14 r ₅ = 73.398 (aspherical surface) d ₅ = 8.08 n ₃ = 1.799 v ₃ = 42.24 r ₆ = -61.14 d ₆ = 3.22 r ₇ = ∞ (aperture) Aspherical surface coefficient E = -0.22175 × 10 ^-6 , F = 0.144242 × 10 ^-8 , G = -0.463
16 × 10 ^-11 H = 0.20141 × 10 ^-13 ｜ x ₁ /f|=2.49×10 ^-5 , ｜ x ₂ /f｜=5.1 × 10 ^-6 f ₁ /f=0.814, f ₁₂ / f =- 1.041, r ₅ /f=0.73
Four

Example 3 f = 100, F / 2.84, 2ω = 65.3 °, f _B = 78.03 r ₁ = 33.178 d ₁ = 13.42 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 59.962 d ₂ = 3.6 r ₃ = -74.411 d ₃ = 2.36 n ₂ = 1.688 v ₂ = 31.08 r ₄ = 38.078 (aspherical surface) d ₄ = 3.03 r ₅ = 80.14 d ₅ = 6.78 n ₃ = 1.799 v ₃ = 42.24 r ₆ = -57.314 d ₆ = 3.22 r ₇ = ∞ (aperture) Aspherical surface coefficient E = 0.10605 × 10 ^-5 , F = -0.70622 × 10 ^-8 , G = 0.2727
4 × 10 ^-10 H = -0.5180 4 × 10 ^-13 │x ₁ /f│=1.33×10 ^-4 , │x ₂ /f│=2.12×10 ^-5 f ₁ /f=0.835, f ₁₂ / f = -1.065, r ₅ /f=0.80
1

Example 4 f = 100, F / 2.8, 2ω = 64.5 °, f _B = 74.712 r ₁ = 29.934 d ₁ = 10.1 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 73 d ₂ = 4.66 r ₃ = -127.88 _{(aspherical) d 3 = 2.34 n 2 =} 1.688 ν 2 = 31.08 r 4 = 28.128 d 4 = 3.94 r 5 = 62.678 d 5 = 9.39 n 3 = 1.799 ν 3 = 42.24 r 6 = -89.484 d 6 = 3.19 r ₇ = ∞ (aperture) Aspherical coefficient E = 0.55462 × 10 ⁻⁶ , F = 0.3249 × 10 ⁻⁸ , G = −0.41347
× 10 ^-11 ｜ x ₁ /f｜=6.14×10 ^-4 , ｜ x ₂ /f｜=2.58×10 ^-5 f ₁ /f=0.629, f ₁₂ /f=-1.409, r ₅ /f=0.62
7

Example 5 f = 100, F / 2.85, 2ω = 64.5 °, f _B = 75.644 r ₁ = 32.153 d ₁ = 11.55 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 96.6 d ₂ = 3.59 r ₃ = -102.656 (aspherical surface) d ₃ = 2.36 n ₂ = 1.688 ν ₂ = 31.08 r ₄ = 32.546 (aspherical surface) d ₄ = 4.13 r ₅ = 92.977 d ₅ = 8 n ₃ = 1.799 ν ₃ = 42.24 r ₆ =- _{74.638 d 6 = 3.21 r 7 =} ∞ ( stop) aspherical coefficients (third ^{surface) E = 0.18226 × 10 -5,} F = 0.26221 × 10 -8 G = -0.23485 × 10 -10, H = 0.41565 × 10 - ¹³ | x ₁ /f|=8.79×10 ^-4 , | x ₂ /f|=6.18×10 ^-5 (4th surface) E = 0.14625 × 10 ^-5 , F = 0.9217 × 10 ^-8 G = -0.81469 × 10 ^-10 , H = 0.1696 × 10 ^-12 | x ₁ /f|=5.67×10 ^-4 , | x ₂ /f|=4.4×10 ^-5 f ₁ /f=0.61, f ₁₂ / f =- 1.891, r ₅ /f=0.93

Example 6 f = 100, F / 2.85, 2ω = 65.2 °, f _B = 78.396 r ₁ = 32.536 d ₁ = 11.69 n ₁ = 1.734 ν ₁ = 51.49 r ₂ = 79.46 d ₂ = 3.42 r ₃ = _{-90.735 d 3 = 2.36 n 2 =} 1.688 ν 2 = 31.08 r 4 = 33.807 d 4 = 3.85 r 5 = 97.281 ( _{aspherical) d 5 = 6.84 n 3 =} 1.799 ν 3 = 42.24 r 6 = -61.291 ( aspherical ) D ₆ = 3.21 r ₇ = ∞ (aperture) aspherical surface coefficient (fifth surface) E = −0.41829 × 10 ⁻⁶ , F = 0.78507 × 10
^-8 G = -0.52193 × 10 ^-10 , H = 0.16729 × 10 ^-12 ｜ x ₁ /f｜=2.79×10 ^-4 , ｜ x ₂ /f｜=3.5×10 ^-6 (6th surface) E = -0.58482 x 10 ^-6 , F = 0.558 x 10 ^-8 G = -0.50279 x 10 ^-10 , H = 0.15504 x 10 ^-12 | x ₁ / f | = 6.26 x 10 ^-5 , | x ₂ / f | = 1.24 × 10 ^-5 f ₁ /f=0.679, f ₁₂ /f=-1.364, r ₅ /f=0.97
3

Example 7 f = 100, F / 2.9, 2ω = 63.6 °, f _B = 74.975 r ₁ = 32.152 d ₁ = 11.55 n ₁ = 1.772 ν ₁ = 49.66 r ₂ = 1117.411 d ₂ = 2.38 r ₃ = -108.998 _{(aspherical) d 3 = 2.90 n 2 =} 1.683 ν 2 = 30.85 r 4 = 32.069 ( _{aspherical) d 4 = 5.24 r 5 =} 108.582 d 5 = 7.33 n 3 = 1.799 ν 3 = 42.24 r 6 = - 86.049 r ₇ = ∞ (aperture) Aspheric coefficient (third surface) E = 0.52883 × 10 ⁻⁵ , F = −0.12305 × 10
^-7 G = 0.25421 × 10 ^-10 , H = −0.26046 × 10 ^-13 ｜ x ₁ /f|=1.79×10 ^-3 , ｜ x ₂ /f|=1.49×10 ^-4 (4th surface) E = 0.48639 x 10 ^-5 , F = -0.36841 x 10
^-9 G = -0.37292 × 10 ^-10 , H = 0.93997 × 10 ^-13 | x ₁ /f|=1.50×10 ^-3 , | x ₂ /f|=1.10×10 ^-4 f ₁ /f=0.541, f ₁₂ /f=−3.231, r ₅ /f=1.09, where r ₁ , r ₂ , ... Are the radii of curvature of each lens surface, d
₁ , d ₂ , ... Is the thickness of each lens and the lens interval, n
₁ , n ₂ , ... Is the refractive index of each lens, ν ₁ , ν ₂ ,.
Is the Abbe number of each lens, and f _B is the back focus.

Further, the shape of the aspherical surface used in the embodiment of the present invention is represented by the following equation, where x is the optical axis direction and y is the direction perpendicular to the optical axis. x = Cy ² / {1+ (1-C ² y ² ) ^1/2 } + Ey ⁴ +
Fy ⁶ + Gy ⁸ + Hy ¹⁰ Here, C is the curvature at the vertex of the aspherical surface (C = 1 / r when the paraxial radius of curvature of the aspherical surface is r), and E, F, G, and H are 4 respectively.
These are aspherical coefficients of the 6th, 6th, 8th, and 10th orders.

[0035]

The triplet lens of the present invention can be used as a bright and high-performance lens system by using aspherical surfaces for the third and subsequent surfaces.

[Brief description of drawings]

FIG. 1 is a sectional view of a triplet lens of the present invention.

FIG. 2 is an aberration curve diagram of Example 1 of the present invention.

FIG. 3 is an aberration curve diagram of Example 2 of the present invention.

FIG. 4 is an aberration curve diagram of Example 3 of the present invention.

FIG. 5 is an aberration curve diagram of Example 4 of the present invention.

FIG. 6 is an aberration curve diagram of Example 5 of the present invention.

FIG. 7 is an aberration curve diagram of Example 6 of the present invention.

FIG. 8 is an aberration curve diagram of Example 7 of the present invention.

Claims (1)

[Claims] 1. A first lens of a positive meniscus lens having a convex surface directed toward the object side and a second lens of a biconcave lens in order from the object side.
A lens, a third biconvex lens, and a diaphragm. At least one surface of the second lens and the third lens is an aspherical surface, and the following conditions (1) and (2) are satisfied. Triplet lens. (1) 1 × 10 ⁻⁵ <| x ₁ / f | <1 × 10 ⁻² (2) 0.5 <r ₅ /f<1.1 where x ₁ is at least one of the aspherical surfaces. The amount of deviation of the aspherical surface from its reference spherical surface at the effective maximum diameter,
r ₅ is the radius of curvature of the object side surface of the third lens, and f is the focal length of the entire system.